Determination of ν2 fundamental band origin for BeH2 and BeD2 from deperturbation analysis of hot bands.

Abstract

New vibration-rotation hot bands, i.e., 031 → 030 and 041 → 040, have been assigned and rotationally analyzed for the gaseous BeH2 molecule. The 03(1)0 (Πu), 03(1)1 (Πg), 04(2)0 (Δg), and 04(2)1 (Δu) states are locally perturbed by the nearby 001 (Σu (+)), 002 (Σg (+)), 01(1)1 (Πg), and 01(1)2 (Πu) states, respectively [A. Shayesteh et al., J. Chem. Phys. 118, 3622 (2003)]. Appropriate Hamiltonian matrices have been constructed to take the effects of rotational ℓ-type doubling, ℓ-type resonance, and third order Coriolis interactions into account, and used in deperturbation analyses. From nonlinear least squares fits of all the data, relative energies and unperturbed rotational constants have been determined for the 030, 031, 040, and 041 vibrational levels of BeH2. Similar deperturbation fits were performed for the 001 → 000 and 011 → 010 bands of the BeD2 isotopologue, while the 030 and 040 vibrational levels were treated as dark states. From relative vibrational energies of the 030 and 040 levels, the ν2 fundamental band origins were determined to be 711.48 ± 0.05 cm(-1) and 548.21 ± 0.1 cm(-1) for BeH2 and BeD2, respectively.